1. Plutonium decays with half life time 24000 years. If Plutonium is stored after 72000 years, the fraction of it that remain :

(a) 1/2

(b) 1/4

(c) 1/8

(d) 1/12

2. A radioactive substance decays to 1/16th of its initial activity in 40 days. the half life of the radioactive substance expressed in day is :

(a) 4

(b) 5

(c) 10

(d) 20

3. The half life time of a radio active elements of x is the same as the mean life of another radioactive element Y. Initially they have same number of atoms, then :

(a) y will decay faster thean x

(b) x will decay faster then y

(c) x and y will decay at the same rate at all time

(d) x and y will decay at the same rate initially

4. A and B are two radioactive substance whose half lives are 1 and 2 years respectively. Initially 10g of A and 1g of B is taken. The time after which they will have same quantity remaining is :

(a) 3.6 years

(b) 7 years

(c) 6.6 years

(d) 5 years

5. What Percent of original radio active substance is left after 5 half life time :

(a) 3%

(b) 5%

(c) 6%

(d) 12%